1. Technical Field
The present disclosure relates generally to laser ablation devices for surgical use. More specifically, the present disclosure relates to laser ablation devices having a longitudinally advancing laser energy transmission mechanism to facilitate ablation of body tissue. The laser ablation device is particularly suited for use in performing transmyocardial revascularization (TMR) and angioplasty.
2. Background of the Related Art
A variety of procedures and apparatus have been developed to treat cardiovascular disease. For example, minimally invasive surgical procedures such as balloon angioplasty and atherectomy have received extensive investigation and are in wide use. In some patients, however, circumstances still require conventional open heart bypass surgery to correct or treat advanced cardiovascular disease. In some circumstances patients may be too weak to undergo the extensive trauma of bypass surgery or repetitive bypasses may already have proved unsuccessful.
An alternative procedure to bypass surgery is transmyocardial revascularization (TMR), wherein holes are formed in the heart wall to provide alternative blood flow channels for ischemic heart tissue. This procedure can be done by laser. In early laser myocardial revascularization, a CO.sub.2 laser was used to produce holes in the heart wall. In this procedure, laser energy is transmitted from the laser to the heart wall by an externally located articulated support. Thus, some surgical opening of the chest wall is required to access the heart muscle. The entrance wound in the heart is closed by external pressure with the objective that the endocardial and myocardial layers remain open to permit blood flow from the ventricle to the heart muscle.
A less traumatic approach to laser myocardial revascularization is disclosed in U.S. Pat. Nos. 5,380,316 and 5,389,096 to Aita et al. These references disclose methods of myocardial revascularization using a deflectable elongated flexible lasing apparatus which is either introduced through a patient's vasculature or alternatively, directly into the patient's chest cavity. The intravascular method requires the direction of laser energy from inside the heart to form a bore in the heart wall while the other method requires introduction of the lasing apparatus through the patient's chest and into contact with the outer wall of the heart.
In both of these methods, the optical fiber conveying the laser energy is advanced and controlled by hand to form the bore. This manual advancement and control presents problems in that depth and rate of penetration are difficult to accurately reproduce for the multiple bores necessary in a myocardial revascularization procedure.
In addition, if the advancement rate of the laser fiber is too slow, tissue damage from thermal and acoustic shock can result. On the other hand, if the advancement rate of the fiber is too fast (i.e., faster than the laser ablation rate), the fiber itself, not the laser energy, can mechanically form at least a portion of the hole, which may be undesirable.
Similar problems are present in other cardiovascular procedures such as, e.g. laser angioplasty wherein an optical fiber is inserted and manually advanced into a patient's vasculature to apply laser energy to obstructions and/or restrictions typically caused by plaque build-up. Both continuous wave and pulsed high energy lasers have been used to provide the vaporizing laser energy. Insuring the plaque is actually ablated and not just pushed aside is important to prevent or delay restenosis. Once again, because the fiber is manually advanced, the rate of advancement of the fiber through the obstruction is generally uncontrolled.